Let's get down to some backup basics. And rule #1 sounds simple, but is a common mistake with serious consequences.
A lot of people make a terrible error with the basic idea of backups that is usually only discovered when it's too late. The absolutely critical rule when it comes to backups is:
It is only a backup when the data lives in more than one place.
Quite often we hear about someone who copied all their digital photos onto a portable hard drive from various cameras and computers "for backup", and then deleted the files from all the cameras and computers too. That big disk of photos might be a nice archive, but it is not a backup.
By all means create a nice, big archive of your photos, or videos, or important work files. And many of these files may no longer be needed on your main computer systems. But once you have your main archive destinations organised, those archives need a second copy kept in a completely different location if you are to consider them backed up.
Remember: one copy is not a backup. It takes two to dance the backup tango.